Two-stage turbochargers are a recent solution to improve engine performance. The large flexibility of these systems, able to operate in different modes, can determine a reduction of the turbo-lag phenomenon and improve the engine tuning. However, the presence of two turbochargers that can be in part operated independently requires effort in terms of analysis and optimization to maximize the benefits of this technology. In addition, the design and calibration of the control system is particularly complex. The transitioning between single stage and two-stage operations poses further control issues.
In this scenario a model-based approach could be a convenient and effective solution to investigate optimization, calibration and control issues, provided the developed models retain high accuracy, limited calibration effort and the ability to run in real time. To this extent, this work documents the development and validation of a control-oriented model of a Diesel engine equipped with two-stage turbocharger. A bottom-up modeling approach, based on the principle of modularity, is adopted to characterize the turbocharger system, as well as the engine airpath, inclusive of a high-pressure EGR loop. The approach characterizes each component as a dynamical system, applying mass and energy conservation laws to derive a set of ordinary differential equations. The reliance on physical principles limits the number of calibration parameters, which can be identified from simple steady-state engine data at few operating points.
The validated model is able to fully characterizing the flows, pressures and temperatures throughout the engine systems. In addition, prediction of engine performance (i.e., torque, BMEP, volumetric efficiency, specific fuel consumption) is provided to support further analysis, optimization and control studies.
